Photoconducting polymers for preparing electrophotographic materials



March 15, 1966 c. J. FOX 3,240,597

PHOTOCONDUCTING POLYMERS FOR PREPARING ELECTROPHOTOGRAPHIC MATERIALS Filed Aug. 21, 1961 11 PHOTOCONDUC TING POLYMER LAYER -/SUPPORT B C IO Charles 0: FOX

INVENTOR.

BY f a ATTORNEYS United States Patent 3 249,597 PHOTUCONDUCTING POLYMERS FOR PREPAR- ING ELECTROPHQTUGRAPHHC MATERIALS Charles J. Fox, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Aug. 21, 1961, Ser. No. 132,713 7 Claims. (Cl. 96-1) This invention relates to electrophotography and more particularly to photoconducting materials for use in processes of electrophotographic reproduction. Still more particularly this invention relates to novel photoconducting polymers for use in preparing photoconductive layers in printing materials useful in processes of electrophotographic reproduction.

Processes of electrophotographic reproduction are well known. The usual process for reproducing an image ac cording to this method comprises forming on the surface of a photoconducting, insulating layer, a uniform electrostatic charge by a suitable means, such as corona discharge, which charge is retained owing to the substantial insulating property of the layer, i.e., the low conductivity of the layer in the dark. The electrostatic charge formed on the surface of the photoconducting layer is then selectively dissipated from the surface of the layer by exposure to light from behind a negative by a conventional exposure operation such as, for example, by contact printing techniques or by lens projection of an image to form a latent image in the photoconducting layer. The latent image pattern produced by charge dissipation in the exposed areas can then be developed, i.e., rendered visible, by a suitable means such as cascading with an electrostatically attractable powder having optical density. It may sometimes be desirable after development to fix the resulting visible image by heating to fuse the powder particles to the surface, in which case, the photoconductive layer itself becomes the final print. In other cases, it may be desirable to use the developed photoconducting layer as a transferring medium to form a final print in a receiving sheet. Of primary concern in the present invention is the use of the present photoconducting materials to form layers comprising the final print.

In preparing the photoconducting layers for use in electrophotography, where a transfer step is employed, or in the present instance where the photoconductive layer becomes the final print, it is desirable that physical smoothness and homogeneity exist in such layers so that unwanted mechanical adhesion of the developer powder does not occur on development to impair definition of the developed image. Very smooth, homogenous coatings of this type have been obtained using certain inorganic photoconductive substances; selenium in particular, but this is accomplished only by vacuum deposition of vaporized selenium upon an electrically conducting support, which process, however, is very lengthy and expensive. In preparing photoconducting layers for use in processes of electrophotography, it is also desirable that the photoconductive substances of such layers comprise substances that have light absorption properties, as well as physical properties for preparing smooth coatings, and further that the absorption characteristics of the photoconducting, insulating layers have an adequate absorption in the visible range of the spectrum.

In the prior art a number of organic substances have been proposed for use in preparing photoconducting layers, however, a number of these substances have shown very low absorption in the visible range of the spectrum and further have not been particularly adapted for producing smooth, homogenous coatings. Another particular difficulty encountered in photoconductive layers prepared using organic substances is that layers of this type have shown a relatively high volatility which results in reduced permanence in the coating.

I have now discovered that photoconductive layers can be prepared using certain low-molecular weight polymers. Moreover that the photoconductive layers prepared using the low molecular weight polymers of this invention are smooth, have a very high degree of homogeneity, and moreover are transparent, and have light absorption characteristics in the visible and near visible region of the spectrum. Accordingly, each of the aforesaid difiiculties are overcome by way of the present invention, and further that the improved coatings provided by the polymer composition can be readily coated on a suitable conducting support to form high grade electrophotographic elements. Another feature embodied in the use of the novel polymeric substances of my invention is that the polymers are readily soluble in particular solvents and can be dried as a layer on a support without recrystallization, which if recrystallization were to occur would leave the surface rough and often opaque as is the case with many of the organic nonpolymeric substances, for example, anthracene and naphthalene.

Accordingly, it is .an object of the present invention to provide novel photoconducting substances. Another object is to provide photoconducting substances which can be used in a photoconducting composition. A further object is to provide such photoconducting substances which can be used to prepare transparent photoconducting layers. Still another object is to provide electrophotographic elements suitable for use in electrophotographic processes wherein the photoconducting layer of said element is of improved smoothness, and has light absorption characteristics in the visible and near visible regions of the spectrum. Still other objects will become apparent from a reading of the specification and appended claims.

The objects of the present invention are accomplished by coating onto an electrically conducting support a photoconductive layer comprising a low-molecular weight photoconductive formaldehyde polymer formed by the condensation of a polynuclear hydrocarbon through formaldehyde in the presence of a strong acid, said polyn-u clear hydrocarbon being selected from the group consisting of polynuclear carbocyclic hydrocarbons and polynuclear azahydrocarbons. The photoconductive formaldehyde polymers of the present invention comprise polymers of relatively low-molecular weight and which are substantially soluble in particular hydrocarbon solvents. According to the present invention, a high degree of solubility is obtained in a composition which is coated onto a suitable support to form the photoconducting layer and there is obtained a smooth, transparent photoconducting layer which comprises a substantial improvement over organic nonpolymeric photoconducting substances hereinbefore described in the prior art.

Members of the class of compounds comprising polynuclear carbocyclic hydrocarbons according :to the present invention comprise for example, anthracene, naphthalene, acenaphthalene, and these compounds having suitable substituents thereon. Suitable su'bstituents which may be attached to the carbocyclic nuclei without detracting from the invention can be seleced from the class comprising an aliphatic group (e.g., methyl, ethyl, propyl, isopropyl, etc.) having from 1 to about 6 carbon atoms, an alkoxy group (e.g., methoxy, ethoxy, etc.), a carbalkoxy group (e.g., carbethoxy, etc), a hydroxyl group, and an amino group.

Members of the class of compounds comprising polynuclear azahydrocarbons according to the present invention comprise for example, N-alkylcarbazole (e.g., N- methylcarbazole, N-ethylcarbazole, N-propyl carbazole, etc.), wherein said alkyl groups have from 1 to about 6 carbon atoms; and N-phenylcarbazole; wherein said compounds have substituents thereon selected from the class 3 comprising an aliphatic group (e.g., methyl, ethyl, propyl, etc.), having from 1 to about 6 carbon atoms, an alkoxy group (e.g., methoxy, ethoxy, propoxy, etc.), a ca'rbalkoxy group (e.g., carbethoxy, etc.), a hydroxyl group, and an amino group.

Other polymeric materials useful in electrophotographic processes comprise: polyvinyland polyacrylyl-derivatives of fused aromatic ring systems such as polyvinylor polyaorylyl-naphthalene or anthracene; polyvinyland polyacryl-derivatives of fused aromatic ring systems conta1ning one or more hetero atoms as exemplified by the polyvinylor 'polyacrylyl-derivatives of acridane, acrrdone, phenothiazine, benzophenothiazine, benzofuran, and polyacrylylcarbazole; polyvinyland polyacrylyl-derivatlves of fused aromatic ring systems containing substituents on the ring or on the polymer chain and which may or may not contain a hetero atom as exemplified by the ring systems previously mentioned; poly-N-substituted acrylamideand methacrylamide-derivatives of the ring systems previously described; polyvinyl alcohol derivatives of the ring systems previously described, such as polyvinylanthral; polyacenaphthalene and copolymers of acenaphthalene with other vinyl compounds, such as styrene; and certain polyesters, polyca rbonates, copolycarbonates and polyamides of fused ring or substituted fused ring compounds which may or may not contain one or more hetero atoms, such as, for example, 2,S-bis hydroxyphenylthiazol-o[5,4-d]thiazole and 2,5-bis(2.-pyridyl) thiazolo[5,4-d]thiazole, which may or may not contain additional electron-donating or electronattracting groups on the phenyl rings.

The manner in which the electrophotographic members of the present invention can be employed to reproduce images thereon will now be further illustrated by reference to the accompanying drawing, wherein:

FIG. 1 is an enlarged sectional view of an electrophotographic member.

FIG. 2 shows a method of placing an electrostatic charge on the surface of the member of FIG. 1.

FIG. 3 shows a method for exposing the charged member of FIG. 2 to pattern illumination in which the charge is electrically dissipated in the illuminated areas.

FIG. 4 shows a method of developing, i.e., render visible, the latent electrostatic image produced by selective illumination as in FIG. 3.

FIG. 5 shows a developed electrophotographic member wherein the member becomes the final print.

More particularly with reference to the accompanying drawing, FIG. 1 shows an electrically conducting support having coated thereon a photoconductive layer 11 comprising a low-molecular weight polymer as hereinbefore described.

FIG. 2 shows the electrophotographic member of FIG. 1 being given a positive electrostatic charge employing a battery 13 or other suitable source of DC. energy, in which wire 12 is connected to the support side 10 of said member and the photoconducting layer 11 is positioned in close proximity with a corona discharge wire connected to said energy source 13 by a conductor wire 14. It is preferable that the source of DC. energy be suitable to maintain a potential of at least 5,000 volts between the corona discharge wire 15 and the support 10. This procedure as well as the procedure shown in FIGS. 3 and 4 are carried out in the dark or in subdued illumination.

FIG. 3 shows a charged electrophotographic member of the present invention comprising a support 10 and photoconducting layer 11 having a positive charge 16 on the surface of said member wherein said member is given a pattern exposure of light and shadow areas as projected through a lens 17 from an original document 18 or other pattern of light and shadow to be recorded. In another method, not shown, the document can be laid directly onto the charged photoconductive layer and suitable exposure applied. Adaptations of this type are known in the art and have been described in a number of U.S. and foreign 4 patents, for example, U.S. Patent 2,693,416, issued November 2, 1954.

FIG. 4 shows a method for applying an electroscopic powder to the latent electrostatic image produced by patterned exposure in FIG. 3. The latent image is made visible by the electrostatically attractable powder 19 being attracted to the unexposed areas of the photoconducting layer 11 which retains its charge. The photoconducting layer is coated on a support 10. A small rotary brush 20 serves to remove loosely-adhering nonelectrostatically attracted powder from the nonirnage areas on the surface of the electrophotographic member. The powder employed may be of any type depending upon the type of print desired, see for example, U.S. Patent 2,297,691, October 6, 1942. Alternatively powders may be employed which possess desirable hydrophilic or hydrophobic properties such that lithographic printing plates can be produced. Other adaptations will be apparent to those skilled in the art. Normally, the more suitable powders are selected from those which have a low melting resin as one component so that by applying suitable thermal exposure to the layer after development, the image areas of the layer can be used to form a final print of good permanence.

FIG. 5 shows an electrophotographic member of the present invention comprising a support 10 and a photoconducting layer 11 having an image 21 thereon in which the member comprises the final print. As indicated elsewhere in this specification, where a suitable transparent support is employed the image produced in FIG. 5 can be utilized as a transparency for further application in photographic processes. Suitable types of transparent supports to which we refer can comprise supporting materials in which transparency exists such as, for example, glass, transparent plastic or film of any desired sort which is either inherently conductive or has a conductive coating on at least one surface thereof. Such a conductive coating is preferably placed between the photoconducting layer and the support. Examples of such materials include glass having a thin layer of silver or some other conductive coating, such as for example, NESA glass having a conductive tin oxide coating thereon (NESA glass is sold by Pittsburgh Plate Glass Company, Pittsburgh, Pennsylvania). Thin foil materials such as aluminum and zinc foil have also a certain degree of transparency and are suitable for use in the invention where transparent prints are desired.

In preparing the low-molecular weight polymers according to the present invention, it is the usual procedure to mix the polynuclear hydrocarbon monomer in a solution comprising formaldehyde or paraformaldehyde and a strong acid. In order that condensation occur and a low-molecular weight polymer be formed, it is necessary that this solution be heated to a temperature in the range from about 100 C. to about 120 C. for a period of from about four hours to about eight hours. ratio of reactants in the condensing mixture can be in the range from about 10:1 to about 1:1 hydrocarbon to formaldehyde in a solution containing from about 40 percent to about percent strong acid. Suitable strong acids can include formic acid, sulfuric acid, hydrochloric acid, acetic acid, chloroacetic acid, etc. The preferred acid comprises formic acid when employed in the concentrated form, for example, in a solution comprising from about percent to about 99 percent formic acid. Depending upon the monomeric component, the acid used, and the ratio of reactants in the formaldehyde condensation process, the conditions of time and temperature can be varied to give optimum polymerization results without the formation of a non-photoconducting insoluble polymer. Normally, however, the formation of a low-molecular weight polymer formed by the process described herein was found to contain from about 2.5 to about 6 molecular units, and to be photoconducting when employed in a dried coating on a support. The

The

polymer was also found to be soluble in a wide variety of hydrocarbon solvents and the photoconducting layers produced therewith were smooth, homogenous, and transparent. Solvents of the type contemplated for use in the present invention can include a wide variety of materials, for example, benzene; toluene; glycol ethers, e.g., dioxane; chlorinated hydrocarbons, e.g., chloroform, methylene chloride, dichloropropane; tetrahydrofuran; etc., and mixtures of such materials. In preparing the photoconducting polymers of the present invention, suitable catalysts can be employed in the process, such as zinc chloride, zinc, and aluminum chloride; however, where formic acid as a concentrated solution is used as the acid source, no separate catalyst appears required. Formic acid presumably acts as its own catalyst for the reaction. The condensation of a polynuclear hydrocarbon with formaldehyde has been described previously in such references as U.S. Patent 2,597,159, May 20 1952, Walker, Formaldehyde, 2nd edition, page 337, Reinhold, New York, 1953, and in Ind. Eng. Chem., 51, page 1275 to 1278, 1959.

To form the photoconductive layers, a short-chain polymer of the present invention is dissolved in a suitable solvent and coated onto an electrically conductive supporting material and dried. Such coatings can be by such methods, for example, as spray-coating, dip-coating, doctor-blade coating, roller-coating, whirl-coating, etc. A useful coating thickness can range from about 0.5 mil to about 6 mils with a preferred thickness in the range from about 1 mil to about 4 mils. In preparing the coating, a binder may be employed. Useful coatings are made where no binder is used; however, where a binder is desired it is required that the binder be compatible with the photoconducting polymer usedand that it be soluble in the solvent used in preparing the coatable composition.

The binders of choice for use in preparing the photoconducting layers should also have a fairly high dielectric strength. Representative binders of this type comprise polystyrene; polypropylene; poly-n-butyl methacrylate; copolymers of vinylacetate and vinyl chloride; styrenealkyd resins; silicone-alkyd resins; soya-alkyd resins; styrene-butadiene copolymers; silicone resins; commercial polyvinyl chloride; polyvinyl acetate; polyester resins; and the like. Materials of this type include such resins as sold under trade names such as Plaskon ST 865, Rezyl 40518, Pliolite S7, Styresol 4440, DC 804, SR-82, Vitel-lOl, etc. The methods of making such resins have been previously described in the prior art, for example, styrene-alkyd resins can be prepared according to the method described in U.S. Patent 2,361,019, October 24, 1944; US. Patent 2,258,423, October 7, 1941; US. Patent 2,453,665, November 9, 1948; etc. Other binders such as paraffin, mineral waxes, etc., can also be employed. These binders are generally characterized as having marked hydrophobic properties, that is are substantially free of water-solubilizing groups such as hydroxyl, free acid groups, amide groups, etc. and as being good electrical insulators and having high electrical resistivity. These binders can be easily dissolved in organic solvents having a boiling point below the charring temperature of a paper support. These binders also are very compatible with the polymeric photoconducting substances of the present invention and accordingly, are readily dispersed therein and form compositions of high homogeneity.

In a particular coating composition for preparing an electrophotographic element according to the present invention, the resinous binder component can be present in an amount in the composition in a range from 0 percent to about 70 percent by weight of the polymeric photoconducting substance. In preparing the coating compositions, it is required that the solvent used be capable of dissolving the components of the composition. Suitable supporting materials for preparing the electrophotographic elements of the invention can comprise, besides the trans- 6 parent supports indicated previously, any of the electrically conducting supports known in the art, for example, paper (at a relative humidity above 30 percent); metal foil, e.g., aluminum foil, zinc foil, etc.; regenerated cellulose and cellulose derivatives; etc.

The photoconductive coatings of the invention can be chemically sensitized to increase the level of sensitivity to light of a given wave length. Preferred sensitizing compounds for this purpose comprise 2,4,7-trinitrofluorenone, and 2,6-diphenyl, 4-anisylthiapyrylium perchlorate and related compounds. Other types of optical sensitization may sometimes also be advantageously employed, for example, where an agent such as an organic dye is used to increase the light-sensitivity to particular regions of the spectrum. Typical organic optical sensitizing dyes include acridine orange, fluorescein, eosin, methylene blue and Rose Bengal.

Two methods have been used to represent the photoelectric or photoconductive speed of the photoconducting layers of the present invention on exposure to light. The first method employed the ratio of the rate of dissipation of electrical charge for the photoconducting layer of the present invention compared to that for a polyvinylcarbazole control layer. An arbitrary value of 1 was assigned to the polyvinylcarbazole layer and the ratio was represented by R+ or R for positively or negatively charged surfaces. The second method employed was termed the tungsten speed for the coating. On this scale, the polyvinylcarbazole layer had a value of 0.03. In either method the coatings were exposed for three seconds through a 0.1 log E stepwedge to a -watt tungsten light source with a filament at 1000 K. through a distance of 1 meter.

The invention will now be illustrated by way of the following examples:

Example 1 A photoconducting polymer prepared from anthracene and paraformaldehyde was prepared as follows for use in a photoconducting layer of an electrophotographic element.

To form the polymer, 0.1 mole of anthracene, i.e., 17.8 grams, was added to a 60 ml. solution of paraformaldehyde, 3.0 grams (0.1 mole) in 98 percent formic acid while stirring at 100 C. The heating at 100 C. was continued for six hours and then the mixture was allowed to cool. The insoluble product was filtered, washed with water, and then washed with ethanol and dried. The product was then dissolved in dioxane and precipitated into ethanol to remove traces of anthracene. After drying, the polymer softened at C. and melted at to 200 C. The cryoscopic molecular weight of the polymer in benzene was found to be 916, which indicated the average length of the polymer chain was 4.7 units.

The polymer formed by the above condensation reaction was then dissolved in chloroform and coated onto a strip of photographic paper (baryta coated) at a thickness of about 3 mils, and then dried overnight at room temperature. Alternately any conducting base, such as aluminum foil, may be used. The coating dried to a clear, smooth, transparent layer. After drying the element was given a blanket positive electrostatic charge by corona discharge, exposed by tungsten illumination either by contact printing or by projecting printing through a transparency, and developed by treating with an electrically attractable electroscopic powder having optical density. The image produced had good resolution and permanence. The coating had a photoelectric speed (R of 0.9 compared to a polyvinyl carbazole coating speed of 1.0.

In preparing typical solutions for coating in preparing the electrophotographic elements of the present invention, the solution prepared for coating on a support according to the invention contain from about 10 to about 40 percent total solids by weight, with a preferred solids content in the range from about 15 to about 25 percent total solids by weight. As indicated hereinbefore, the total solids content of a particular composition prepared for coating can comprise photoconductive polymer alone or photoconductive polymer in admixture with a suitable resinous binder.

Example 2 An electrophotographic element was prepared as follows.

To 100 ml. of a 20 percent tetrahydrofuran solution containing grams of the condensation polymer of Example 1, was added 10 grams of a copolymer of vinyl chloride and vinyl acetate to serve as binder. The solution was then coated onto a paper support and dried overnight at room temperature to remove the tetrahydrofuran solvent. After drying the slightly off-white-to yellow coating was charged under a positive corona in subdued illumination. The charged element was then exposed and developed as in Example 1 to give an image of good resolution and permanence. The photoelectric speed of the coating was 0.9 relative to a polyvinyl carbazole coating having a photoelectric speed of 1.0.

When an electrophotographic element was prepared as above using 4.5 grams of the condensation polymer of Example 1 and 10 grams of polystyrene to serve as a binder and coated from a percent solution in chloroform, the three second tungsten speed of the coating was about 0.1, compared to a polyvinyl carbazole coating having a tungsten speed of 0.03. Incorporation of two mole percent of 2,4,7-trinitrofiuorenone based on the photoconductive polymer in the above photoconducting coating increased the three second tungsten speed to a value of 3.0. An image of good resolution and permanence was obtained.

Example 3 An electrophotographic element was prepared using a photoconducting polymer formed from N-ethyl carbazole and paraformaldehyde according to the following procedure.

3.5 grams (0.018 mole) of N-ethyl carbazole was added to a ml. solution of 99 percent formic acid containing 0.9 gram (0.3 mole) of paraformaldehyde. The mixture was then heated to 100 C. and held at this temperature while stirring for six hours. A solvent-insoluble polymeric solid was formed which was recovered and washed was water, ethanol and acetone and thereafter dried. The polymer was then purified by precipitation with ethanol in tetrahydrofuran.

The polymer formed was analyzed and found to contain no more than 0.2 percent oxygen and hence the absence of hydroxyl end groups in the polymer. The cryoscopic molecular weight in benzene was found to be 597, which indicated that the polymer had an average chain length of about 2.9 units. This polymer was used to prepare a photoconducting layer as in Example 2 using a copolymer of vinyl chloride-vinyl acetate as binder. The layer was then exposed and developed as in Example 1 to produce an image having good resolution and permanence.

The photoelectric speed of polymeric photoconducting layers of this example was (R+) 2.0 for positively-charged coatings and (R) 5.0 for negatively-charged coatings relative to a speed of 1.0 for a polyvinyl carbazole coating.

Example 4 An electrophotographic element was prepared using a photoconducting polymer prepared from acenaphthene and paraformaldehyde.

15.4 grams (0.1; mole) of acenaphthene was added to m1. of 99 percent formic acid solution containing 3.0 grams (0.1 mole) of paraformaldehyde. The mixture was heated at 100 C. for six hours while stirring. The polymer formed was isolated, washed with water, ethanol 8 and acetone and then dried. Analysis of the polymer corresponded to a polymer chain three units in length.

The polymer formed by this example was then dissolved at 10 grams concentration in ml. of benzene. To the solution was then added 10 grams of poly-n-butylmethacrylate. The solution was then coated at 3 mils thickness onto an aluminum foil support. The element was then allowed to dry overnight at room temperature to remove the benzene. The dried coating was very smooth and transparent.

The electrophotographic element was then charged, exposed and developed according to previous examples to give an image of good resolution and permanence. The photoelectric speed of the coating was 0.2 for either positive or negative charged coatings relative to a speed of 1.0 for polyvinyl carbazole.

The advantages of the present invention are immediately apparent in terms of the application of the present compounds as novel photoconducting polymers in the preparation of electrophotographic printing materials. Particularly advantageous in this regard is that electrophotographic coatings which employ polymeric photoconductors have lower volatility than coatings employing nonpolymeric organic photoconductors and accordingly coatings of the present polymeric photoconductor type have a much longer shelf-life or permanence. Further advantages are apparent as regards the present invention when one considers the improvements obtained hereby in obtaining very smooth, homogenous and transparent coatings which have the improved permanence hereinbefore described. Transparency in a coating is very desirable because of the latitude which it introduces into the material. For example, transparency in a coating makes possible the use of images obtained in such coatings as intermediate originals, both in contact or projection type copying processes. The images produced according to the present process can be fixed by heating, or a transfer of the image areas can be made to a receiving sheet. By a wise choosing of the electroscopic powders for use in developing the latent electrostatic images in the charged plates, printing masters such as hectographic masters, lithographic masters, half-tone reproductions etc., can be prepared. The manner in which the present photoconducting polymers may be employed to this end is well know in the art and has been described in such US. patents as 2,297,691, issued October 6, 1942.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the scope and spirit of the invention, as described hereinabove and as defined in the appended claims.

I claim:

1. An electrophotographic process comprising the steps of exposing an electrostatically charged photoconductive insulating layer to a light pattern to form an electrostatic image on said layer and developing the image on said layer by applying electrostatically attractable particulate material, said photoconductive insulating layer comprising a photoconductive, low molecular weight condensation polymer of formaldehyde and a polynuclear aromatic monomer selected from the group consisting of (A) anthracene, naphthalene, acenaphthalene and substitution products thereof wherein said substituents are selected from the group consisting of alkyl, alkoxy, and hydroxy. and

(B) N-alkyl carbazole, N-phenyl carbazole and substitution products thereof wherein said substituents are selected from the group consisting of alkyl, alkoxy, carbalkoxy, and hydroxy.

2. The process of claim 1 wherein said photoconductive layer consists essentially of said photoconductive condensation polymer and minor amounts of sensitizing compounds.

3. The process of claim 1 wherein said photoconductive layer comprises at least 30% by Weight of said photoconductive condensation polymer, the remainder of said layer consisting essentially of an insulating resin binder and minor amounts of sensitizing compounds.

4. The process of claim 1 wherein said aromatic monomer is anthracene.

5. The process of claim 1 wherein said aromatic monomer is N-ethyl carbazole.

6. The process of claim 1 wherein said aromatic monomer is acenaphthalene.

7. The process of claim 1 wherein said photoconductive low molecular weight condensation polymer contains about 3 to 6 aromatic monomer units.

References (Cited by the Examiner UNITED STATES PATENTS 1,587,274 6/1926 Beebe et al. 260-67 2,697,028 12/1954 Baker 96-1 10 2,958,676 11/1960 Krzikalla et al. 260-67 3,025,160 3/1962 Bunge et al. 961 3,037,861 6/1962 Hoegl et al. 96-1 3,041,165 6/1962 Sus et al. 96-1 FOREIGN PATENTS 562,336 5/1958 Belgium.

319,444 9/1929 Great Britain.

680,343 10/1952 Great Britain.

OTHER REFERENCES NORMAN G. TORCHIN, Primary Examiner.

ABRAHAM H. WINKELSTEIN, A. LOUIS MONA- CELL, Examiners. 

1. AN ELECTROPHOTOGRAPHIC PROCESS COMPRISING THE STEPS OF EXPOSING AN ELECTROSTATICALLY CHARGED PHOTOCONDUCTIVE INSULATING LAYER TO A LIGHT PATTERN TO FORM AN ELECTROSTATIC IMAGE ON SAID LAYER AND DEVELOPING THE IMAGE ON SAID LAYER BY APPLYING ELECTROSTATICALLY ATTRACTABLE PARTICULATE MATERIAL, SAID PHOTOCINDUCTIVE INSULATING LAYER COMPRISING A PHOTOCONDUCTIVE, LOW MOLECULAR WEIGHT CONDENSATION POLYMER OF FORMALDEHYDE AND A POLYNUCLEAR AROMATIC MONOMER SELECTED FROM THE GROUP CONSISTING OF (A) ANTHRACENE, NAPHTHALENE, ACENAPHTHALENE AND SUBSTITUTION PRODUCTS THEREOF WHEREIN SAID SUBSTITUENTS ARE SELECTED FROM THE GROUP CONSISTING OF ALKYL, ALKOXY, AND HYDROXY, AND (B) N-ALKYL CARBAZOLE, N-PHENYL CARBAZOLE AND SUBSTITUTION PRODUCTS THEREOF WHEREIN SAID SUBSTITUENTS ARE SELECTED FROM THE GROUP CONSISTING OF ALKYL, ALKOXY, CARBALKOXY, AND HYDROXY. 